Re: next/master bisection: baseline.login on rk3288-rock2-square

From: Ard Biesheuvel <ardb@kernel.org>
To: Guillaume Tucker <guillaume.tucker@collabora.com>
Cc: "kernelci-results@groups.io" <kernelci-results@groups.io>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Nicolas Pitre <nico@fluxnic.net>,
	Linus Walleij <linus.walleij@linaro.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: next/master bisection: baseline.login on rk3288-rock2-square
Date: Sat, 6 Feb 2021 14:12:55 +0100	[thread overview]
Message-ID: <CAMj1kXEeTH2sHPEd2P+qh3G6uzHubREVA3v6iVvo_X4iCEVGZQ@mail.gmail.com> (raw)
In-Reply-To: <7ed6fae6-eee8-5751-352b-f735ffb83194@collabora.com>

On Sat, 6 Feb 2021 at 14:10, Guillaume Tucker
<guillaume.tucker@collabora.com> wrote:
>
> On 05/02/2021 12:05, Ard Biesheuvel wrote:
> > On Fri, 5 Feb 2021 at 09:21, Ard Biesheuvel <ardb@kernel.org> wrote:
> >>
> >> On Thu, 4 Feb 2021 at 22:31, Guillaume Tucker
> >> <guillaume.tucker@collabora.com> wrote:
> >>>
> >>> On 04/02/2021 18:23, Nick Desaulniers wrote:
> >>>> On Thu, Feb 4, 2021 at 10:12 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >>>>>
> >>>>> On Thu, Feb 04, 2021 at 10:06:08AM -0800, 'Nick Desaulniers' via Clang Built Linux wrote:
> >>>>>> On Thu, Feb 4, 2021 at 8:02 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >>>>>>>
> >>>>>>> On Thu, 4 Feb 2021 at 16:53, Guillaume Tucker
> >>>>>>> <guillaume.tucker@collabora.com> wrote:
> >>>>>>>>
> >>>>>>>> On 04/02/2021 15:42, Ard Biesheuvel wrote:
> >>>>>>>>> On Thu, 4 Feb 2021 at 12:32, Guillaume Tucker
> >>>>>>>>> <guillaume.tucker@collabora.com> wrote:
> >>>>>>>>>>
> >>>>>>>>>> Essentially:
> >>>>>>>>>>
> >>>>>>>>>>   make -j18 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- LLVM=1 CC="ccache clang" zImage
> >>>>>>
> >>>>>> This command should link with BFD (and assemble with GAS; it's only
> >>>>>> using clang as the compiler.
> >>>>>
> >>>>> I think you missed the 'LLVM=1' before CC="ccache clang". That should
> >>>>> use all of the LLVM utilities minus the integrated assembler while
> >>>>> wrapping clang with ccache.
> >>>>
> >>>> You're right, I missed `LLVM=1`. Adding `LD=ld.bfd` I think should
> >>>> permit fallback to BFD.
> >>>
> >>> That was close, except we're cross-compiling with GCC for arm.
> >>> So I've now built a plain next-20210203 (without Ard's fix) using
> >>> this command line:
> >>>
> >>>     make LD=arm-linux-gnueabihf-ld.bfd -j18 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- LLVM=1 CC="ccache clang" zImage
> >>>
> >>> I'm using a modified Docker image gtucker/kernelci-build-clang-11
> >>> with the very latest LLVM 11 and gcc-8-arm-linux-gnueabihf
> >>> packages added to be able to use the GNU linker.  BTW I guess we
> >>> should enable this kind of hybrid build setup on kernelci.org as
> >>> well.
> >>>
> >>> Full build log + kernel binaries can be found here:
> >>>
> >>>     https://storage.staging.kernelci.org/gtucker/next-20210203-ard-fix/v5.10-rc4-24722-g58b6c0e507b7-gtucker_single-staging-41/arm/multi_v7_defconfig/clang-11/
> >>>
> >>> And this booted fine, which confirms it's really down to how
> >>> ld.lld puts together the kernel image.  Does it actually solve
> >>> the debate whether this is an issue to fix in the assembly code
> >>> or at link time?
> >>>
> >>> Full test job details for the record:
> >>>
> >>>     https://lava.collabora.co.uk/scheduler/job/3176004
> >>>
> >>
> >>
> >> So the issue appears to be in the way the linker generates the
> >> _kernel_bss_size symbol, which obviously has an impact, given that the
> >> queued fix takes it into account in the cache_clean operation.
> >>
> >> On GNU ld, I see
> >>
> >>    479: 00065e14     0 NOTYPE  GLOBAL DEFAULT  ABS _kernel_bss_size
> >>
> >> whereas n LLVM ld.lld, I see
> >>
> >>    433: c1c86e98     0 NOTYPE  GLOBAL DEFAULT  ABS _kernel_bss_size
> >>
> >> and adding this value may cause the cache clean to operate on unmapped
> >> addresses, or cause the addition to wrap and not perform a cache clean
> >> at all.
> >>
> >> AFAICT, this also breaks the appended DTB case in LLVM, so this needs
> >> a separate fix in any case.
> >
> > I pushed a combined branch of torvalds/master, rmk/fixes (still
> > containing my 9052/1 fix) and this patch to my for-kernelci branch
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/
> >
> > Guillaume,
> >
> > It seems there is no Clang-11 coverage there, right? Mind giving this
> > branch a spin? If this fixes the regressions, we can get these queued
> > up.
>
> That's right, Clang builds are only enabled on linux-next and
> mainline at the moment.  We could enable it on any other branch
> where it makes sense.  How about just the main defconfig for arm,
> arm64 and x86_64 on your ardb/for-kernelci branch?
>

Yes, please.

> For now I've run another set of builds with clang-11 and got the
> following test results with your branch on staging:
>
>   https://staging.kernelci.org/test/job/ardb/branch/for-kernelci/kernel/v5.11-rc6-146-g923ca344043a/plan/baseline/
>
> which are all passing.
>
> I'll reply to the thread with your patch to confirm.
>

Excellent, thanks a lot.

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